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A method for rate selection by a communication device for enhanced uplink
during soft handoff in a wireless communication system includes a first
step of receiving information from a scheduler. This information can
included one or more of scheduling, a rate limit, a power margin limit,
and a persistence. A next step includes determining a data rate for an
enhanced uplink during soft handoff using the information. A next step
includes transmitting to a serving base station on an enhanced uplink
channel at the data rate determined from the determining step.

1. A method for rate selection by a communication device for uplink
transmission during soft handoff in a wireless communication system, the
method comprising steps of: receiving information from a scheduler;
determining a data rate for an uplink transmission using the information;
and transmitting to a serving base station on an uplink channel at the
data rate determined from the determining step.

2. The method of claim 1, wherein the receiving step includes receiving a
rate limit from the serving base station, and the determining step
includes using the rate limit and local channel conditions to determining
the data rate for the uplink channel.

3. The method of claim 1, wherein the receiving step includes receiving a
power margin limit from the serving base station, and the determining
step includes using the power margin limit and local channel conditions
to determining the data rate for the uplink channel.

4. The method of claim 2, wherein the receiving step includes receiving
interference rise-over-thermal limits from a plurality of Active Set base
stations, and wherein the determining step includes determining the
highest rate that meets the rate limit and interference limits of the
plurality of Active Set base stations given local conditions of the
uplink channel.

5. The method of claim 2, wherein the receiving step includes receiving
power control commands from a plurality of Active Set base stations and
storing the received commands as a power control command history, and
wherein the determining step includes determining the highest rate that
meets the rate limit using the power control command history for the
plurality of Active Set base stations.

6. The method of claim 2, wherein the receiving step includes receiving
and measuring channel signal strength levels from a plurality of Active
Set base stations and storing the strength levels, and wherein the
determining step includes determining the highest rate that meets the
rate limit using the stored channel signal strength levels for the
plurality of Active Set base stations.

9. The method of claim 1, wherein the receiving step includes receiving a
rate limit from the scheduler for autonomous transmissions.

10. The method of claim 1, wherein the receiving step includes receiving a
power margin limit from the scheduler for autonomous transmissions

11. The method of claim 9, wherein the receiving step includes receiving
an persistence information on a control channel from the scheduler.

12. The method of claim 11, wherein the control channel is a common
broadcast control channel.

13. The method of claim 11, wherein the receiving step includes receiving
a maximum uplink data channel to pilot channel ratio, and the persistence
value is based on rise-over-thermal information from the Active Set of
base station cells.

14. The method of claim 11, wherein the receiving step includes receiving
a maximum power margin, and the persistence value is based on
rise-over-thermal information from the Active Set of base station.

15. The method of claim 1, wherein the receiving step includes receiving
time constraints for autonomous transmissions from the scheduler, that
splits the explicit scheduling into separate times from autonomous
scheduling.

16. The method of claim 15, wherein the time constraints for autonomous
transmissions from the scheduler are determined based on the number of
users in autonomous mode.

17. The method of claim 15, wherein the time constraints for autonomous
transmissions are determined based on the number of users in explicit
scheduling mode.

18. The method of claim 15, wherein the time constraints for autonomous
transmissions are determined based on the buffer occupancy of the
autonomous mode and explicit scheduling mode users.

19. A method for rate selection by a communication device for uplink
during soft handoff in a communication system, the method comprising
steps of: receiving a scheduling assignment message including a power
margin limit from a scheduler; determining a data rate for an uplink
transmission during soft handoff using the power margin limit, local
channel conditions and a buffer occupancy of the communication device;
and transmitting to a serving base station on an uplink channel at the
data rate determined from the determining step.

20. The method of claim 19, wherein the receiving step includes receiving
a scheduling assignment message including a rate limit from a scheduler.

21. The method of claim 19, wherein the determining step includes
determining a maximum rate for an enhanced uplink during soft handoff
using the rate limit, local channel conditions and a buffer occupancy of
the communication device.

22. The method of claim 19, wherein the receiving step includes receiving
an interference rise-over-thermal requirement from the serving Active Set
base station and a plurality of adjacent Active Set base stations, and
wherein the determining step includes determining the highest rate that
meets the received power margin limit and interference limits given local
conditions of the uplink channel.

23. The method of claim 19, wherein the receiving step includes receiving
power control commands from the serving Active Set base station and a
plurality of Active Set base stations and storing the received commands
as a power control command history, and wherein the determining step
includes determining the highest rate that meets the power margin limit
using the power control command history for the Active Set base stations.

24. The method of claim 19, wherein the receiving step includes receiving
and measuring common pilot channel signal strength levels from a
plurality of adjacent Active Set base stations and storing the strength
levels, and wherein the determining step includes determining the highest
rate that meets the power margin limit using the stored common pilot
channel signal strength levels for the plurality of Active Set base
stations.

25. The method of claim 19, wherein the determining step includes a data
rate constraint of K2*P.sub.margin.sub..sub.--.sub.limit/P.sub.dpcch*TPC_-
correction where P.sub.margin.sub..sub.--.sub.limit is the power margin
limit, P.sub.dpcch is a power of the downlink physical control channel,
and K2 is a scale factor, and TPC_correction dependent upon a power
control command history and pilot channel signal strength.

26. The method of claim 19, wherein the determining step includes updating
the power margin limit to account for changes in a serving cell reverse
link interference rise-over-thermal.

27. The method of claim 19, wherein the determining step includes a data
rate constraint of R.sub.max.sub..sub.--.sub.effective.sub..sub.--.sub.SH-
Otarget*g(imbalance) where R.sub.max.sub..sub.--.sub.effective.sub..sub.---
.sub.SHOtarget is the maximum effective rate, and g(imbalance) is an
imbalance between a transmission gain of the scheduling cell and
communication device, divided by a transmission gain between an adjacent
cell with next largest or largest transmission gain relative to
scheduling cell and the communication device.

28. A method for rate selection by a communication device for enhanced
uplink during soft handoff in a UMTS communication system, the method
comprising steps of: receiving a scheduling assignment message including
a a power margin limit from a scheduling base station; determining a
maximum data rate for an enhanced uplink during soft handoff using the
power margin limit, local channel conditions and a buffer occupancy of
the communication device; and transmitting to a serving base station on
an enhanced uplink channel at the data rate determined from the
determining step.

29. The method of claim 28, wherein the receiving step includes receiving
a scheduling assignment message including a rate limit from a scheduling
base station.

30. The method of claim 28, wherein the determining step includes
determining a maximum rate for an enhanced uplink during soft handoff
using the rate limit, local channel conditions and a buffer occupancy of
the communication device.

31. The method of claim 28, wherein the receiving step includes receiving
interference rise-over-thermal limits from a scheduling base station and
a plurality of Active Set base stations, and wherein the determining step
includes determining the highest rate that meets the power margin limit
and interference limits of the scheduling base station and plurality of
Active Set base stations given local conditions of the enhanced uplink
channel.

32. The method of claim 28, wherein the receiving step includes receiving
power control commands from the scheduling base station and a plurality
of Active Set base stations and storing the received commands as a power
control command history, and wherein the determining step includes
determining the highest rate that meets the power margin limit using the
power control command history for the scheduling base station and the
plurality of Active Set base stations.

33. The method of claim 28, wherein the receiving step includes receiving
and measuring common pilot channel signal strength levels from the
scheduling base station and a plurality of Active Set base stations and
storing the strength levels, and wherein the determining step includes
determining the highest rate that meets the power margin limit using the
stored common pilot channel signal strength levels for the scheduling
base station and plurality of Active Set base stations.

Description

FIELD OF THE INVENTION

[0001] The present invention relates generally to a wireless communication
device, and more specifically to choosing a rate for an enhanced uplink
during soft handoff in a communication system.

BACKGROUND OF THE INVENTION

[0002] In a Universal Mobile Telecommunications System (UMTS), such as
that proposed for the next of the third generation partnership project
(3GPP) standards for the UMTS Terrestrial Radio Access Network (UTRAN),
such as wideband code division multiple access (WCDMA) or cdma2000 for
example, user equipment (UE) such as a mobile station (MS) communicates
with any one or more of a plurality of base station subsystems (BSSs)
dispersed in a geographic region. Typically, a BSS (known as Node-B in
WCDMA) services a coverage area that is divided up into multiple sectors
(known as cells in WCDMA). In turn, each sector is serviced by one or
more of multiple base transceiver stations (BTSs) included in the BSS.
The mobile station is typically a cellular communication device. Each BTS
continuously transmits a downlink (pilot) signal. The MS monitors the
pilots and measures the received energy of the pilot symbols.

[0003] In a cellular system, there are a number of states and channels for
communications between the MS and the BSS. For example, in IS95, in the
Mobile Station Control on the Traffic State, the BSS communicates with
the MS over a Forward Traffic Channel in a forward link and the MS
communicates with the BSS over a Reverse Traffic Channel in a reverse
link. During a call, the MS must constantly monitor and maintain four
sets of pilots. The four sets of pilots are collectively referred to as
the Pilot Set and include an Active Set, a Candidate Set, a Neighbor Set,
and a Remaining Set, where, although the terminology may differ, the same
concepts generally apply to the WCDMA system.

[0004] The Active Set includes pilots associated with the Forward Traffic
Channel assigned to the MS. This set is active in that the pilots and
companion data symbols associated with this set are all actively combined
and demodulated by the MS. The Candidate Set includes pilots that are not
currently in the Active Set but have been received by the MS with
sufficient strength to indicate that an associated Forward Traffic
Channel could be successfully demodulated. The Neighbor Set includes
pilots that are not currently in the Active Set or Candidate Set but are
likely candidates for handoff. The Remaining Set includes all possible
pilots in the current system on the current frequency assignment,
excluding the pilots in the Neighbor Set, the Candidate Set, and the
Active Set.

[0005] When the MS is serviced by a first BTS, the MS constantly searches
pilot channels of neighboring BTSs for a pilot that is sufficiently
stronger than a threshold value. The MS signals this event to the first,
serving BTS using a Pilot Strength Measurement Message As the MS moves
from a first sector serviced by a first BTS to a second sector serviced
by a second BTS, the communication system promotes certain pilots from
the Candidate Set to the Active Set and from the Neighbor Set to the
Candidate Set. The serving BTS notifies the MS of the promotions via a
Handoff Direction Message. Afterwards, for the MS to commence
communication with a new BTS that has been added to the Active Set before
terminating communications with an old BTS, a "soft handoff" will occur.

[0006] For the reverse link, typically each BTS in the Active Set
independently demodulates and decodes each frame or packet received from
the MS. It is then up to a switching center or selection distribution
unit (SDU) normally located in a Base Station Site Controller (BSC),
which is also known as a Radio Network Controller (RNC) in WCDMA
terminology, to arbitrate between the each BTS's decoded frames. Such
soft handoff operation has multiple advantages. Qualitatively, this
feature improves and renders more reliable handoff between BTSs as a MS
moves from one sector to the adjacent one. Quantitatively soft-handoff
improves the capacity/coverage in a cellular system. However, with the
increasing amount of demand for data transfer (bandwidth), problems can
arise.

[0007] Several third generation standards have emerged, which attempt to
accommodate the anticipated demands for increasing data rates. At least
some of these standards support synchronous communications between the
system elements, while at least some of the other standards support
asynchronous communications. At least one example of a standard that
supports synchronous communications includes cdma2000. At least one
example of a standard that supports asynchronous communications includes
WCDMA.

[0008] While systems supporting synchronous communications can sometimes
allow for reduced search times for handover searching and improved
availability and reduced time for position location calculations, systems
supporting synchronous communications generally require that the base
stations be time synchronized. One such common method employed for
synchronizing base stations includes the use of global positioning system
(GPS) receivers, which are co-located with the base stations that rely
upon line of sight transmissions between the base station and one or more
satellites located in orbit around the earth. However, because line of
sight transmissions are not always possible for base stations that might
be located within buildings or tunnels, or base stations that may be
located under the ground, sometimes the time synchronization of the base
stations is not always readily accommodated.

[0009] However, asynchronous transmissions are not without their own set
of concerns. For example, the timing of uplink transmissions in an
environment supporting MS autonomous scheduling (whereby a MS may
transmit whenever the MS has data in its transmit buffer and all MSs are
allowed to transmit as needed) by the individual MSs can be quite
sporadic and/or random in nature. While traffic volume is low, the
autonomous scheduling of uplink transmissions is less of a concern,
because the likelihood of a collision (i.e. overlap) of data being
simultaneously transmitted by multiple MSs is also low. Furthermore, in
the event of a collision, there are spare radio resources available to
accommodate the need for any retransmissions. However, as traffic volume
increases, the likelihood of data collisions (overlap) also increases.
The need for any retransmissions also correspondingly increases, and the
availability of spare radio resources to support the increased amount of
retransmissions correspondingly diminish. Consequently, the introduction
of explicit scheduling (whereby a MS is directed by the network when to
transmit) by a scheduling controller can be beneficial.

[0010] However even with explicit scheduling, given the disparity of start
and stop times of asynchronous communications and more particularly the
disparity in start and stop times relative to the start and stop times of
different uplink transmission segments for each of the non-synchronized
base stations, gaps and overlaps can still occur. Both gaps and overlaps
represent inefficiencies in the management of radio resources (such as
rise over thermal (ROT), a classic and well-known measure of reverse link
traffic loading in CDMA systems), which if managed more precisely can
lead to more efficient usage of the available radio resources and a
reduction in the rise over thermal (ROT).

[0011] For example, FIG. 1 is a block diagram of communication system 100
of the prior art. Communication system 100 can be a cdma2000 or a WCDMA
system. Communication system 100 includes multiple cells (seven shown),
wherein each cell is divided into three sectors (a, b, and c). A BSS
101-107 located in each cell provides communications service to each
mobile station located in that cell. Each BSS 101-107 includes multiple
BTSs, which BTSs wirelessly interface with the mobile stations located in
the sectors of the cell serviced by the BSS. Communication system 100
further includes a radio network controller (RNC) 110 coupled to each BSS
and a gateway 112 coupled to the RNC. Gateway 112 provides an interface
for communication system 100 with an external network such as a Public
Switched Telephone Network (PSTN) or the Internet.

[0012] The quality of a communication link between an MS, such as MS 114,
and the BSS servicing the MS, such as BSS 101, typically varies over time
and movement by the MS. As a result, as the communication link between MS
114 and BSS 101 degrades, communication system 100 provides a soft
handoff (SHO) procedure by which MS 114 can be handed off from a first
communication link whose quality has degraded to another, higher quality
communication link. For example, as depicted in FIG. 1, MS 114, which is
serviced by a BTS servicing sector b of cell 1, is in a 3-way soft
handoff with sector c of cell 3 and sector a of cell 4. The BTSs
associated with the sectors concurrently servicing the MS, that is, the
BTSs associated with sectors 1-b, 3-c, and 4-a, are known in the art as
the Active Set of the MS.

[0013] Referring now to FIG. 2, a soft handoff procedure performed by
communication system 100 is illustrated. FIG. 2 is a block diagram of a
hierarchical structure of communication system 100. As depicted in FIG.
2, RNC 110 includes an ARQ function 210, a scheduler 212, and a soft
handoff (SHO) function 214. FIG. 2 further depicts multiple BTSs 201-207,
wherein each BTS provides a wireless interface between a corresponding
BSS 101-107 and the MSs located in a sector serviced by the BSS.

[0014] When performing a soft handoff, each BTS 201, 203, 204 in the
Active Set of the MS 114 receives a transmission from MS 114 over a
reverse link of a respective communication channel 221, 223, 224. The
Active Set BTSs 201, 203, and 204 are determined by SHO function 214.
Upon receiving the transmission from MS 114, each Active Set BTS 201,
203, 204 demodulates and decodes the contents of a received radio frame.

[0015] At this point, each Active Set BTS 201, 203, 204 then conveys the
demodulated and decoded radio frame to RNC 110, along with related frame
quality information. RNC 110 receives the demodulated and decoded radio
frames along with related frame quality information from each BTS 201,
203, 204 in the Active Set and selects a best frame based on frame
quality information. Scheduler 212 and ARQ function 210 of RNC 110 then
generate control channel information that is distributed as identical
pre-formatted radio frames to each BTS 201, 203, 204 in the Active Set.
The Active Set BTSs 201, 203, 204 then simulcast the pre-formatted radio
frames over the forward link.

[0016] Alternatively, the BTS of the current cell where the MS is camped
(BTS 202) can include its own scheduler and bypass the RNC 110 when
providing scheduling information to the MS. In this way, scheduling
functions are distributed by allowing a mobile station (MS) to signal
control information corresponding to an enhanced reverse link
transmission to Active Set base transceiver stations (BTSs) and by
allowing the BTSs to perform control functions that were previously
supported by a RNC. The MS in a SHO region can choose a scheduling
assignment corresponding to a best Transport Format and Resource
Indicator information (TFRI) out of multiple scheduling assignments that
the MS receives from multiple Active Set BTS. As a result, the enhanced
uplink channel can be scheduled during SHO, without any explicit
communication between the BTSs. In either case, explicit transmit power
constraints (which are implicit data rate constraints) are provided by a
scheduler, which are used by the MS 114, along with control channel
information, to determine what transmission rate to use.

[0017] As proposed for the UMTS system, a MS can use an enhanced uplink
dedicated transport channel (EUDCH) to achieve an increased uplink data
rate. The MS must determine the data rate to use for the enhanced uplink
based on local measurements at the MS and information provided by the
scheduler and must do so during soft handoff such that the interference
level increase at adjacent cells (other than Active Set cells) is not so
large that uplink voice and other signaling coverage is significantly
reduced.

[0018] In practice, when an MS is explicitly scheduled (Explicit Mode) by
the BTS, for example, to use the enhanced uplink channel, or when a MS
autonomously decides when to transmit data (Autonomous mode), the MS must
determine a transmission rate given the constraints of a maximum rate or
equivalently a maximum power margin indicated by the scheduler and the
amount of data in its buffer. This is particularly important when the MS
is in a multi-coverage area served by multiple cells where, in a CDMA
system, such a MS is typically in soft handoff (SHO) with any of the said
multiple cells if more than one are members of the MS's current Active
Set. However, the prior art does not consider the amount of interference
created during soft handoff and its affect on adjacent cells.

[0019] Hence, in determining a maximum transmission rate on an EUDCH, a
need exists for MS to consider the impact on all adjacent cells
(typically cells in its active or neighbor set), and not just the best
serving or scheduling Active Set cell, such that uplink voice and other
signaling coverage is not significantly impacted. It would also be of
benefit if the MS could take into account corrections due to power
control commands from the BTS. It would also be an advantage to account
for imbalances between transmission gains between the MS and its
scheduled or target cell and non-scheduled or non-target cells.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The features of the present invention, which are believed to be
novel, are set forth with particularity in the appended claims. The
invention, together with further objects and advantages thereof, may best
be understood by reference to the following description, taken in
conjunction with the accompanying drawings, in the several figures of
which like reference numerals identify like elements, and in which:

[0021] FIG. 1 is a block diagram of an exemplary communication system of
the prior art;

[0022] FIG. 2 is a block diagram of a hierarchical structure of the
communication system of FIG. 1;

[0023] FIG. 3 depicts a distributed network architecture in accordance
with an embodiment of the present invention;

[0024] FIG. 4 is a message flow diagram with frame format information in
accordance with an embodiment of the present invention;

[0025] FIG. 5 is a block diagram of a communication system in accordance
with an embodiment of the present invention;

[0026] FIG. 6 is an exemplary illustration of a map included in a
scheduling assignment in accordance with an embodiment of the present
invention; and

[0027] FIG. 7 is an exemplary illustration of a map included in a
scheduling assignment in accordance with another embodiment of the
present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0028] The present invention provides for a mobile station to determine a
maximum transmission rate on an enhanced uplink channel while also
considering the impact on all adjacent cells (typically cells in its
active or neighbor set), and not just the best serving (target cell) or
scheduling Active Set cell, such that uplink voice and other signaling
coverage is not significantly impacted. The present invention also takes
into account corrections due to power control commands from the BTS, not
only from the scheduling cell but also the Active Set of cells. Further,
the present invention takes advantage of imbalances between transmission
gains between the MS and its scheduled or target cell and non-scheduled
or non-target cells.

[0029] The present invention supports Active Set handoff and scheduling
functions by allowing a mobile station (MS) to signal control information
corresponding to an enhanced reverse link transmission to Active Set BTSs
and a scheduler that performs control functions. Generally, an embodiment
of the present invention encompasses a method for rate selection by a
communication device for uplink transmissions in a communication system.
The method includes steps of receiving information from a scheduler,
determining a power and/or a data rate for uplink transmissions during
soft handoff using the information, and transmitting to the base station
on an uplink channel at the power and/or data rate determined from the
determining step.

[0030] In practice, the scheduling information received by the mobile
station includes the uplink channel scheduling assignment from the
scheduler, wherein the uplink channel scheduling assignment can include
at least one of a sub-frame assignment, a maximum power margin target, a
maximum power level target, and a maximum transport format related
information. Moreover, the present invention includes preliminary steps
of receiving scheduling information by a BTS from a MS, wherein the
scheduling information includes at least one of a queue status and a
power status of the mobile station, and determining an uplink channel
scheduling assignment for the selected mobile station using at least one
of the scheduling information and a base station interference metric and
an uplink quality corresponding to the selected mobile station. The
method further includes a step of transmitting to a serving base station
on an enhanced uplink channel at the data rate determined from the
determining step.

[0031] More specifically, the information in the receiving step can
include one or more of a scheduling assignment, a rate limit, a power
margin limit, interference rise-over-thermal limits from a plurality of
Active Set base stations, a stored history of power control commands from
a plurality of Active Set base stations, measured common pilot channel
signal strength levels from a plurality of Active Set base stations, time
constraints, and a persistence value. In addition, the determining step
uses any of the above information, along with local channel conditions
and buffer size to determining the maximum data rate for the enhanced
uplink channel.

[0032] The present invention may be more fully described with reference to
FIGS. 3-7. FIG. 5 is a block diagram of a communication system 1000 in
accordance with an embodiment of the present invention. Preferably,
communication system 1000 is a Code Division Multiple Access (CDMA)
communication system, such as cdma2000 or Wideband CDMA (WCDMA)
communication system, that includes multiple communication channels. Each
communication channel comprises an orthogonal code, such as a Walsh code,
that is different from and orthogonal to an orthogonal code associated
with each of the other communication channels. However, those who are of
ordinary skill in the art realize that communication system 1000 may
operate in accordance with any one of a variety of wireless communication
systems, such as a Global System for Mobile communication (GSM)
communication system, a Time Division Multiple Access (TDMA)
communication system, a Frequency Division Multiple Access (FDMA)
communication system, or an Orthogonal Frequency Division Multiple Access
(OFDM) communication system.

[0033] Similar to communication system 100, communication system 1000
includes multiple cells (seven shown). Each cell is divided into multiple
sectors (three shown for each cell--sectors a, b, and c). A base station
subsystem (BSS) 1001-1007 located in each cell provides communications
service to each mobile station located in that cell. Each BSS 1001-1007
includes multiple base stations, also referred to herein as base
transceiver stations (BTSs) or Node-Bs, which wirelessly interface with
the mobile stations located in the sectors of the cell serviced by the
BSS. Communication system 1000 further includes a RNC 1010 coupled to
each BSS, preferably through a 3GPP TSG UTRAN Iub Interface, and a
gateway 1012 coupled to the RNC. Gateway 1012 provides an interface for
communication system 1000 with an external network such as a Public
Switched Telephone Network (PSTN) or the Internet.

[0034] Referring now to FIGS. 3 and 5, communication system 1000 further
includes at least one mobile station (MS) 1014. MS 1014 may be any type
of wireless user equipment (UE), such as a cellular telephone, a portable
telephone, a radiotelephone, or a wireless modem associated with data
terminal equipment (DTE) such as a personal computer (PC) or a laptop
computer. Note that MS, UE, and user are used interchangeably throughout
the following text. MS 1014 is serviced by multiple BTSs, that are
included in an Active Set associated with the MS. MS 1014 wirelessly
communicates with each BTS in communication system 1000 via an air
interface that includes a forward link (from the BTS to the MS) and a
reverse link (from the MS to the BTS). Each forward link includes
multiple forward link control channels, a paging channel, and traffic
channel. Each reverse link includes multiple reverse link control
channels, a paging channel, and a traffic channel. However, unlike
communication system 100 of the prior art, each reverse link of
communication system 1000 further includes another traffic channel, an
Enhanced Uplink Dedicated Transport Channel (EUDCH), that facilitates
high speed data transport by permitting a transmission of data that can
be dynamically modulated and coded, and demodulated and decoded, on a
sub-frame by sub-frame basis.

[0035] Communication system 1000 includes a soft handoff (SHO) procedure
by which MS 1014 can be handed off from a first air interface whose
quality has degraded to another, higher quality air interface. For
example, as depicted in FIG. 5, MS 1014, which is serviced by a BTS
servicing sector b of cell 1, is in a 3-way soft handoff with sector c of
cell 3 and sector a of cell 4. The BTSs associated with the sectors
concurrently servicing the MS, that is, the BTSs associated with sectors
1-b, 3-c, and 4-a, are the Active Set of the MS. In other words, MS 1014
is in soft handoff (SHO) with the BTSs 301, 303, and 304, associated with
the sectors 1-b, 3-c, and 4-a servicing the MS, which BTSs are the Active
Set of the MS. As used herein, the terms `Active Set` and `serving,` such
as an Active Set BTS and a serving BTS, are interchangeable and both
refer to a BTS that is in an Active Set of an associated MS. Furthermore,
although FIGS. 3 and 5 depict BTSs 301, 303, and 304 as servicing only a
single MS, those who are of ordinary skill in the art realize that each
BTS 301-307 may concurrently schedule, and service, multiple MSs, that
is, each BTS 301-307 may concurrently be a member of multiple Active
Sets.

[0036] FIG. 3 depicts a network architecture 300 of communication system
1000 in accordance with an embodiment of the present invention. As
depicted in FIG. 3, communication system includes multiple BTSs 301-307,
wherein each BTS provides a wireless interface between a corresponding
BSS 1001-1007 and the MSs located in a sector serviced by the BTS.
Preferably, a scheduling function 316, an ARQ function 314 and a SHO
function 318 are distributed in each of the BTSs 301-307. RNC 1010 is
responsible for managing mobility by defining the members of the Active
Set of each MS serviced by communication system 1000, such as MS 1014,
and for coordinating multicast/multireceive groups. For each MS in
communication system 1000, Internet Protocol (IP) packets are multi-cast
directly to each BTS in the Active Set of the MS, that is, to BTSs 301,
303, 304 in the Active Set of MS 1014.

[0037] Preferably, each BTS 301-307 of communication system 1000 includes
a SHO function 318 that performs at least a portion of the SHO functions.
For example, SHO function 318 of each BTS 301, 303, 304 in the Active Set
of the MS 1014 performs SHO functions such as frame selection and
signaling of a new data indicator. Each BTS 301-307 can include a
scheduler, or scheduling function, 316 that alternatively can reside in
the RNC 110. With BTS scheduling, each Active Set BTS, such as BTSs 301,
303, and 304 with respect to MS 1014, can choose to schedule the
associated MS 1014 without need for communication to other Active Set
BTSs based on scheduling information signaled by the MS to the BTS and
local interference and SNR information measured at the BTS. By
distributing scheduling functions 306 to the BTSs 301-307, there is no
need for Active Set handoffs of a EUDCH in communication system 1000. The
ARQ function 314 and AMC function, which functionality also resides in
RNC 110 of communication system 100, can also be distributed in BTSs
301-307 in communication system 1000. As a result, when a data block
transmitted on a specific Hybrid ARQ channel has successfully been
decoded by an Active Set BTS, the BTS acknowledges the successful
decoding by conveying an ACK to the source MS (e.g. MS 1014) without
waiting to be instructed to send the ACK by the RNC 1010.

[0038] In order to allow each Active Set BTS 301, 303, 304 to decode each
EUDCH frame, MS 1014 conveys to each Active Set BTS, in association with
the EUDCH frame, modulation and coding information, incremental
redundancy version information, HARQ status information, and transport
block size information from MS 1014, which information is collectively
referred to as transport format and resource-related information (TFRI).
The TFRI only defines rate and modulation coding information and H-ARQ
status. The MS 1014 codes the TFRI and sends the TFRI over the same frame
interval as the EUDCH.

[0039] By providing MS 1014 signaling of the TFRI corresponding to each
enhanced reverse link transmission to the Active Set BTSs 301, 303, 304,
the communication system 1000 can support HARQ, AMC, Active Set handoff,
and scheduling functions in a distributed fashion. As described in
greater detail below, the communication system 1000 allows Active Set
BTSs 301, 303, 304 to provide an efficient control channel structure to
support scheduling, HARQ, AMC functions for an enhanced reverse link, or
uplink, channel in order to maximize throughput, and enables an MS in a
SHO region to choose a scheduling assignment corresponding to the best
TFRI out of multiple assignments it receives from multiple Active Set
BTS.

[0040] Referring now to FIG. 4, a message flow diagram 400 illustrates an
exchange of communications between an MS of communication system 1000,
such as MS 1014, and each of the multiple BTSs included in an Active Set
of the MS, that is, BTSs 301, 303, and 304. MS 1014 communicates
scheduling information 402 to each Active Set BTS 301, 303, 304 using a
first reverse link control channel 406 with a known fixed modulation and
coding rate and transport block size. A corresponding code assignment for
the first reverse link control channel is done on a semi-static basis.
Preferably, MS 1014 does not transmit control information when the MS's
corresponding data queue is empty.

[0041] Each Active Set BTS 301, 303, 304 receives scheduling information
402 from the MS 1014 serviced by the BTS via the first reverse link
control channel 406. The scheduling information 402 may include the data
queue status and the power status of the MS. Based on the scheduling
information 402 received from each MS serviced by a BTS, each serving, or
Active Set, BTS 301, 303, 304 schedules one or more of the MSs serviced
by the BTS, that is, MS 1014, for each scheduling transmission interval
410.

[0042] Each Active Set BTS 301, 303, 304 uses reverse link interference
level, MS scheduling information 402, and power control information to
determine a maximum allowed power margin target or limit for each MS 1014
serviced by the BTS. Power margin may be defined as the difference
between a current DPCCH power level and the maximum power level supported
by the MS. Or it may be defined as the difference between a current DPCCH
power level and the maximum allowed EUDCH power level. The reverse link
pilot is used for demodulation purposes such as automatic frequency
control, synchronization, and power control. For example, in a WCDMA
system the reverse link pilot is carried on the reverse link DPCCH.
Finally, power margin can also be defined as in equation (1) below.

[0043] Upon choosing an MS (e.g. MS 1014) to be scheduled, each Active Set
BTS 301, 303, 304 conveys a scheduling assignment 418 to the chosen MS,
such as MS 1014, on a first forward link control channel 426. The
scheduling assignment 418 consists of the maximum allowed `power margin`
limit or target and a map of the allowed EUDCH sub-frame transmission
intervals, such as a 2 ms sub-frame interval, for the next 10 ms
transmission interval (also known as a scheduling interval) using a first
forward link control channel 426. Note a map is not needed if the
transmission interval is the same as the sub-frame transmission interval.

[0044] FIG. 6 illustrates an example of the map included in the scheduling
assignment 418 (FIG. 4). Column 1205 comprises a set of state indicators
showing which EUDCH sub-frames that MS 1014 can use during an assigned
scheduling transmission interval 1210, for example scheduling
transmission interval 410 of FIG. 4. In another embodiment of the present
invention, the scheduling assignment 418 of FIG. 4 may further include a
physical channel Walsh code assignment, also referred to herein as a
second forward link control channel code (SFLCCH_code) of a second
forward link control channel 420 or secondary common control physical
channel (S-CCPCH) of FIG. 4. The map can also include a TFRI assignment
for each EUDCH sub-frame, that is, a TFRI sub-frame corresponding to each
EUDCH sub-frame. An example of such a map is shown in FIG. 7, which again
includes the column of state indictors 1205 and a column of TFRI values
1315. Each Active Set BTS 301, 303, 304 also uses the second forward link
control channel 420 to convey ACK/NAK information to the MS related to
the MS's EUDCH sub-frame transmissions.

[0045] Each Active Set BTS 301, 303, 304 creates an MS identifier (ID)
that is uniquely associated with an MS serviced by the BTS, that is MS
1014, for the first forward link control channel 426. The BTS creates the
MS ID by running an n-bit ID that is uniquely associated with the MS (and
known at the MS and the Active Set BTSs) through a CRC generator at the
BTS. Use of the MS ID by the BTS allows the associated MS to determine
when the scheduling assignment 418 sent on the first forward control
channel 426 is meant for the MS. The first forward link control channel
426 can use the 10 ms frame format depicted in FIG. 4, which format
includes a scheduling assignment 418, tail bits, and a CRC.
Alternatively, the first forward link control channel 426 frame size may
use a frame format of 2 ms. The first forward link control channel 426 is
staggered to avoid additional latency.

[0046] An MS in a SHO region, such as MS 1014, may receive one or more
scheduling assignments 418 from one or more Active Set, or serving, BTSs
301, 303, 304. When the MS receives more than one scheduling assignment,
the MS may select a scheduling assignment 418 corresponding to the best
TFRI. The MS determines the TFRI for each EUDCH sub-frame 422 based on
the interference information (maximum allowed power margin limit) from
the selected scheduling assignment 418 and the current scheduling
information 402 measured at the MS, that is, current data queue and power
status or power margin. The MS then enables a fast power control function
and the feedback rate is then performed on a slot-by-slot basis, for
example, 1500 Hz in the case of 3GPP UMTS. The MS then transmits the
EUDCH sub-frame 422 to the Active Set BTSs 301, 303, 304 using the
selected TFRI.

[0047] There are several considerations in choosing the maximum rate of
data transmitted on the EUDCH. In accordance with the present invention,
a MS can determine its EUDCH transmission rate using one or more of a
maximum power margin limit, amount of data in the MS transmission buffer,
current maximum available power margin, the power control command history
received from each Active Set cell, and the current common pilot strength
level from each Active Set cell. Note from this point forward cell and
sector will be used interchangeably and both refer to the sector of any
BSS. Any of these considerations can be used to set the maximum data
rate. Therefore, the present invention chooses the minimum value of the
chosen constraints to set the maximum data rate.

[0048] The maximum power margin limit (P.sub.margin.sub..sub.--.sub.limit)
is sent by the scheduler (or UTRAN) to the MS. The power margin is as
defined in equation (1) below. The power margin is the available MS power
after accounting for the power requirements of control channels (DPCCH,
HS-DPCCH) and other higher priority channels such as a DPDCH which may
serve as a reference bearer. The maximum power margin limit can be sent
in scheduling assignment information, such as being sent in a scheduling
assignment message (SAM) from the scheduling BTS or sent on the S-CCPCH.
For explicit scheduling one or more BTS can schedule one or more MSs to
transmit on a given time interval by sending a SAM on a dedicated channel
or a common code channel. For autonomous scheduling a power margin limit
and persistence is sent either via dedicated channels or broadcast using
S-CCPCH. P.sub.margin.sub..sub.--.sub.limit is based on scheduling
information, which can include buffer occupancy (BO) and current power
margin, provided by MS to the Active Set BTSs as scheduling information
(SI). For explicit scheduling the BTS (given the SI from all the MSs it
serves and the local information such as interference rise over thermal
noise (RoT)) decides when and which mobiles will transmit. For autonomous
scheduling the mobile decides when to transmit on the enhanced uplink
channel using persistence and power margin limit information provided by
the Active Set BTSs. Preferably, the MS is additionally constrained to
specific time periods (sub-frames) along with other mobiles in the
autonomous scheduling mode. The MS initiates the move to autonomous mode
from explicit mode and there is handshaking involved between the MS and
the BTS during the mode transitions. P.sub.margin.sub..sub.--.sub.limit
can also be based on loading information, such as RoT measurements and
other local information such as received pilot SNR (DPCCH)) at the
scheduling BTS.

[0049] The current maximum available power margin (P.sub.margin) is
defined as

[0050] where .beta..sub.hs-dpcch is the power ratio of HS-DPCCH/DPCCH. The
high speed dedicated physical control channel (HS-DPCCH) is a physical
channel introduced for HSDPA in 3GPP release 5. It carries the C/I
feedback information (CQI) and ACK/NAK information to support H-ARQ and
fast scheduling and rate assignment), and .beta..sub.dpdch=DPDCII/DPCCH
power ratio.

[0051] In a preferred embodiment, the present invention accounts for
adjacent cell interference during SHO. In particular the MS can use the
power control command history received from each Active Set cell,
including the scheduling cell, and/or the current common pilot strength
level from each Active Set cell.

[0052] Given the information above, along with the amount of data in the
transmit buffer of the MS, there are five main steps to computing the
maximum allowed UE rate (R.sub.max.sub..sub.--.sub.allowed.sub..sub.--.su-
b.UE) in accordance with the present invention, which is eventually
signaled to the Active Set BTSs on the enhanced uplink control channel
E-DPCCH (e.g. TFRI) where its transmission start time can proceed the
EUDCH transmission start time.

[0053] In a first step, the maximum achievable rate
(R.sub.max.sub..sub.--.sub.achievable) is computed by the following
equation:

[0055] where R.sub.reference.sub..sub.--.sub.bearer is the reference
bearer rate, and .beta..sub.preference.sub..sub.--.sub.bearer is the
reference bearer power to DPCCH power ratio of the reference bearer whose
frame erasures are used to drive the outer loop (e.g. the reference
bearer could be a 7.95 Kbps speech service). The reference bearer is a
physical channel with known rate and a CRC (or a other hard or soft
pass/fail decoding check herein referred to as frame quality information)
that drives outer loop power control. Outer loop power control controls
an inner loop setpoint (also known as an outer loop threshold) based on
frame quality information. The inner loop setpoint is used to set the
power control commands used for fast (inner loop) power control).
.DELTA..sub.Eb/Nt is the Eb/Nt difference in dB between the enhanced
uplink channel for a particular rate and frame error rate (FER) target
level and the reference bearer channel and its FER target level.

[0056] Alternatively, one could use null frames, which is when a CRC is
rate matched over a 10 or 20 ms DPDCH TTI (voice or data frame). This
would change the value of the terms determining K1 (i.e.
.DELTA..sub.Eb/Nt, R.sub.reference.sub..sub.--.sub.bearer, and
.beta..sub.reference.sub..sub.--.sub.bearer). Finally, it is possible to
just fix the innerloop setpoint to map the pilot (DPCCH) Ec/Nt to a fixed
level (-28 dB e.g.), which must be communicated to MS at call setup. This
option of fixing the inner loop setpoint would be used if there were no
other service (such as speech) and one decided not to use the null frame
approach.

[0057] Eb/Nt requirement difference (based on performance requirements for
channels given in the specification and refined by testing) is determined
between reference bearer and the EUDCH given their corresponding FER
targets. For each FER target desired for the enhanced uplink channel
(EUDCH) a corresponding Eb/Nt is determined. This is compared to the
Eb/Nt requirement for the reference bearer channel's FER target level
(which typically will be around 2%). Hence, .DELTA..sub.Eb/Nt is the
Eb/Nt difference in dB between the enhanced uplink channel for a
particular rate and FER target level and the reference bearer channel and
its FER target level. Typically, a Eb/Nt delta table is created since
there maybe multiple FER targets for a given enhanced uplink rate as well
as multiple rates.

[0058] Afterwards, the required EUDCH to pilot power ratio,
.beta..sub.eudch, is determined for the EUDCH selected rate
(R.sub.max.sub..sub.--.sub.achievable). The EUDCH to pilot power ratio is
a function of the EUDCH rate. Typically, the ratio is about 4 dB for a 10
kbps rate and increases by 10log10 (Reudch/10 kbps) as R.sub.eudch
exceeds 10 kbps. The relationship can be refined based on link testing
and measurements. Tables with these power ratios exist in the 3GPP2
specifications for convolutional and turbo encoded channels for different
rates and different FER targets. Determining .beta..sub.eudch implies
that an iterative solution is required for K1 since .DELTA..sub.Eb/Nt is
a function of R.sub.max.sub..sub.--.sub.achievable. That is, an iterative
solution is implied since the maximum achievable rate for the EUDCH
(R.sub.max.sub..sub.--.sub.achievable) is an unknown to solve for, and
.beta..sub.eudch is an unknown on the right side of the equation
dependent on it. Alternatively, it might be possible to eliminate this by
solving for R.sub.max.sub..sub.--.sub.achievable/.beta..sub.eudch. As an
example the resulting equation can be computed as:

where K1=R.sub.reference.sub..sub.--.sub.bearer*.DELTA..sub.Eb/Nt/.beta..s-
ub.reference.sub..sub.--.sub.bearer

[0059] In a second step, the rate necessary to exhaust the buffer
(R.sub.exhaust) for the scheduled (explicit mode) or desired (autonomous
mode) transmission interval is computed, as is known in the art, as.

[0060] For example, if there where 2000 bytes in the buffer and the
transmission interval was 10 ms then the R.sub.exhaust=2000*8/0.01=1.6
Mbps.

[0061] In a third step, the maximum power margin limit
(P.sub.margin.sub..sub.--.sub.limit) is updated to account for changes in
the scheduling (explicit mode) or targeted (autonomous mode) serving
cell's reverse link rise over thermal (RoT) so that the maximum allowed
rate for the scheduling cell (R.sub.max.sub..sub.--.sub.allowed) can be
computed. The scheduling cell sends an explicit scheduling assignment to
the MS for when to transmit so it may be the only cell guaranteed to be
listening for the MS's transmission. The target cell, in the case of
autonomous mode, is the one the MS thinks is the best serving cell based
on pilot measurements and power control command history. This update or
correction to P.sub.margin.sub..sub.--.sub.limit is called TPC
correction, in accordance with the present invention. To compute the
correction the power control commands of the scheduled or targeted
serving cells (depending on scheduling mode) can be integrated from a
time corresponding to when the scheduling assignment message (SAM) was
transmitted by the UTRAN to a present time in order to adjust the
P.sub.margin limit. Since the MS is power controlled its current power
margin moves closer or farther away from this limit as each new power
control command is received.

[0062] Note that without any TPC corrections the maximum allowed rate
indicated by the UTRAN would be calculated as:

[0063] However, the present invention accounts for corrections due to TPC
commands and pilot Ec/Nt measurements from each Active Set serving cell
(including a scheduling or targeted cell (ST) and non-scheduling or
non-targeted cell (NSNT)) by applying a TPC correction to
R.sub.max.sub..sub.--.sub.allowed as follows:

[0072] where .beta. and .lambda. are scale factors. For example,
.beta.=0.5 and .lambda.=1.0.

[0073] The summing operation occurs over a previous time period defined as
the time the SAM was transmitted to the time it is received at the MS or
alternatively from the time the power margin limit was actually computed
at the BTS to the time it is received at the MS or in another alternative
embodiment the summing operation occurs from the time the power margin
was actually computed at the BTS to the time just prior to when the MS
make its rate decision.

[0074] In Case A, a scheduling or target serving cell's power control
command history indicates an increase in RoT. For example, consecutive
power control up-commands are received from the scheduling or target
serving cell or alternatively the power control commands are integrated
over the previous time period and result in a significant increase in the
inner loop power adjustment or alternatively the current power gain level
of the DPCCH (which accounts for both inner loop power adjustment and the
current open loop power adjustment)shows a significant net increase over
the previous time period while the other non-scheduling or non-target
serving cell's power control command history indicates a reduction in RoT
over the same previous time period. Since the power control bits from the
weaker non-scheduling BTS cells are likely unreliable the TPC_Correction2
is only used in the limited imbalance cases (e.g. less than 4 dB
imbalance). It is important to note that the TPC bits could all indicate
power up from a weak leg, which typically occurs with link imbalance of 4
dB or more. Using information in this latter imbalance case would produce
erroneous results. Note that when the MS is not in soft handoff
TPC_Correction2=1.0.

[0075] In Case B, a pilot from strongest cell site is more than a
predetermined amount (e.g. 3 dB) higher than the scheduling site.

[0076] Alternatively, given an average (over 30 slots, for example where a
slot is 0.67 ms) of common downlink pilot Ec/Nt of the scheduling or
target site, and the other serving Active Set cells, then the following
rules can be used to compute R.sub.max allowed:

[0080] where the previous rules for K2, TPC_correction, and
TPC_correction2 apply.

[0081] In a fourth step, a maximum allowed SHO rate
(R.sub.max.sub..sub.--.sub.sho) is computed which keeps the interference
at a level that keeps acceptable voice and signaling coverage at adjacent
cells when the SHO MS transmits on the E-DCH. Since all users are power
controlled to arrive at the minimum power required to achieve a targeted
FER, and typically the rate of each user is known, then it is possible to
compute what the rise will be if another user at a specific rate with
some required FER target level is added. The interference assessment is
assisted by RoT measurements taken periodically by each BTS. In the case
described here, a BTS does not know if a user controlled by an adjacent
cell will transmit and at what rate. However, with the control scheme of
the present invention, a BTS only needs minimum margin (e.g. effectively
one or two voice users) to account for users scheduled by adjacent BTSs.
That is, it is desired that the interference contribution to adjacent
cells by the SHO MS be effectively only one or two 12.2 kbps users when
not DTX'ed. For example, speech users do not always transmit at 12.2 kbps
(or at other rates associated with the chosen AMR vocoder rate). When
there is no perceptible speech, transmission ceases (DTX) or
transmissions continue where only a CRC rate match across the entire
frame interval (TTI) is sent which allows outer loop power control to
continue operation. Also SID (silence indicator descriptor) frames are
periodically sent during DTX mode. Hence, equation (9), shown below,
starts at the maximum effective rate (R.sub.max.sub..sub.--.sub.effective-
.sub..sub.--.sub.SHOtarget), which effects the amount of overhead the
scheduler BTS needs to account for in determining the maximum power
margin limit (P.sub.margin.sub..sub.--.sub.limit), and allows an increase
in the maximum effective rate the larger the link imbalance gets.

[0082] (e g. R.sub.max.sub..sub.--.sub.effective.sub..sub.--.sub.SHOtarget-
=12.2 kbps) where imbalance=scheduling cell's link transmission (linear)
gain (or path loss between BTS and MS including antenna gains) between it
and MS divided by the adjacent cell transmission gain (between it and MS)
with next largest or largest transmission gain relative to scheduling
cell's link transmission gain and can be estimated by:

[0083] Where Pilot Ec/Nt.sub.NSNTi is the pilot Ec/Nt of non-serving or
non-target cell i.

[0084] The function, g(.), can be a direct mapping, e.g.
g(imbalance)=1*imbalance, or it can be more complicated where the go
causes the imbalance to be limited and/or scaled.

[0085] R.sub.max.sub..sub.--.sub.effective SHOtarget can be chosen based
on current loading of the scheduling BTS, assuming that adjacent cells
are similarly loaded, or it can be fixed to a relatively low data rate
corresponding to one or two speech users. The MS knows the loading on the
scheduling cell from the power margin limit sent in the SAM (or via
S-CPCCH for autonomous scheduling) which indicates changes in loading can
be accounted for as discussed above with power control information. The
power margin limit computed by a BTS can be set to account for adjacent
cell RoT loading. If adjacent cells are not heavily loaded this will show
up indirectly in the RoT thermal measurements of the cell in question.
Also, periodically the RNC (CBSC) will send down information for
computing the power margin limit or an adjustment for the power margin
limit for each cell based on the RoT thermal measurements that are
periodically sent from each BTS to the RNC and/or based on the number of
active users in the adjacent cells. The R.sub.max.sub..sub.--.sub.effecti-
ve.sub..sub.--.sub.SHOtarget is a system parameter that can be set
conservatively (e.g. one or two speech users) especially if there is no
RNC feedback (i.e. information passed down to help set the power margin
limit) or more aggressively especially with RNC feedback. The average of
the aggregate number of HARQ retransmission for users scheduled by a
given BTS can also be used to dynamically adjust R.sub.max.sub..sub.--.su-
b.effective.sub..sub.--.sub.SHOtarget.

[0089] This would be more useful determination of the allowable or maximum
allowable enhanced uplink rate when the user is not in soft handoff.

[0090] In another embodiment of the present invention, a persistence
parameter (p) is defined and broadcast over the cell, for additional use
in controlling data rates, as well as power, in autonomous mode. In
autonomous scheduling all MSs are allowed to transmit simultaneously, but
their data rates and powers are controlled by the BTS. In the prior art,
the maximum data rate, or equivalently referred to as the
T/P.sub.max.sub..sub.--.sub.auto, is updated by the BTS every frame or
sub-frame and the information is conveyed to the individual MS using a
dedicated downlink control channel. In particular, this can be done by
restrictions in the Transport Format Combination (TFC) Set imposed by the
BTS. One way to convey the information is to puncture some bits in the
downlink DCH. This however, will degrade the performance of existing
channels and power offset for these un-coded bits should be set at a
considerably higher value in some cases (e.g. soft handoff). In contrast,
the present invention addresses an efficient way of changing the maximum
data rate using the broadcast channel (e.g. Forward Access Channel (FACH)
transmitted on the secondary common control physical channel (S-CCPCH))
and the use of the persistence parameter to compute the enhanced uplink
rate in the autonomous mode.

[0091] In the autonomous mode the MS can transmit, without request, up to
the power margin limit (P.sub.margin limit.sub..sub.--.sub.auto). As
before power margin is defined by

[0092] or in an alternative embodiment up to a maximum T/P ratio (EUDCH to
Pilot ratio) where the P.sub.margin.sub..sub.--.sub.limit.sub..sub.--.sub-
.auto or T/P.sub.max.sub..sub.--.sub.auto is set by the BTS through layer
one (L1) signaling. In the case of WCDMA the uplink pilot channel is
carried on the DPCCH code channel. In this mode, the BTS provides the MS
with an allowed TFC subset from which the MS's TFC selection algorithm
selects a TFC to be used by employing the TFC selection method defined in
3GPP specifications. This TFC subset provided by the BTS is named the "UE
allowed TFC subset".

[0093] The present invention addresses an efficient way of changing the
P.sub.margin.sub..sub.--.sub.limit.sub..sub.--.sub.auto using the FACH
transmitted on the secondary common control physical channel (S-CCPCH)
when the MS is transmitting in the autonomous mode. Further, this
invention also proposes to have the MS transmit in autonomous mode in
predefined n consecutive sub-frames only (asynchronous nature of MS). The
sub-frames in which MS is allowed to transmit in autonomous mode are
assigned by the RNC. However, the signaling for the autonomous mode can
be made at any point of time. This helps when the MS is in soft-handoff.
The length of the autonomous mode time interval, in terms of n
consecutive sub-frames, and the repetition rate of the autonomous mode
time interval can be based on the number of users in autonomous mode, the
number of users in explicit scheduling mode, or the number of user in
autonomous and explicit scheduling mode. The buffer occupancy and rate of
change in buffer occupancy of the users can also be considered in
determining the autonomous mode time interval length and repetition rate
of the time interval. For example, the autonomous mode time interval
length could range from 2 to 10 frames (or sub-frames) and the repetition
rate could be once every 30 frames (or sub-frames) and the range of the
repetition rate could be from 2 to 100 frames (or sub-frames).

[0094] In practice, at the BTS, adjacent cells periodically provide
updates of their current load to the scheduler or RNC. Note BTS and cell
are used interchangeably in the following text. The scheduler or RNC
transmits the above mentioned information to the BTS's periodically (e.g.
500 msec). The BTS computes a persistence value (p) based on the ROT at
the source BTS and the ROT of the adjacent cells sent by the scheduler or
RNC. The "persistence" is generally a non-negative integer and lies
between 0 and 1. The BTS also computes P.sub.margin.sub..sub.--.sub.limit-
.sub..sub.--.sub.auto which based on the ROT information for the source
cell and adjacent cells. The (P.sub.margin.sub..sub.--.sub.limit.sub..sub-
.--.sub.auto)i from each cell i is computed for each MS and the minimum
value is selected for broadcast transmission, i.e.
P.sub.margin.sub..sub.--.sub.limit.sub..sub.--.sub.auto=MIN[(P.sub.margin-
.sub..sub.--.sub.limit.sub..sub.--.sub.auto)1, (P.sub.margin.sub..sub.--.s-
ub.limit.sub..sub.--.sub.auto)2, . . . ]. These two parameters are updated
every frame. The persistence value and P.sub.margin.sub..sub.--.sub.limit-
.sub..sub.--.sub.auto are broadcast using FACH which is carried on the
secondary common control physical channel (S-CCPCH) every frame. In an
alternative embodiment the persistence value and the
P.sub.margin.sub..sub.--.sub.limit.sub..sub.--.sub.auto can also be sent
on the dedicated channel for each user.

[0095] Specifically, the BTS computes P.sub.margin.sub..sub.--.sub.limit.s-
ub..sub.--.sub.auto by first receiving a power margin (P.sub.margin)
measurement that is sent periodically to the BTS by each UE (MS).
P.sub.margin is defined as P.sub.margin=Max_UE_Pwr-P.sub.DPCCH(1+a.sub.1+-
a.sub.2+a.sub.3) where a.sub.1=.beta..sub.dpdch/.beta..sub.dpcch,
a.sub.2=.beta..sub.hs-dpcch/.beta..sub.dpcch and a.sub.3=.beta..sub.other-
cod.sub..sub.--.sub.mux.sub..sub.--.sub.ch/.beta..sub.dpcch. Then
E.sub.c(DPCCH)/N.sub.t of the pilot bits for each MS is measured at BTS.
The maximum SNR supported by each MS is then given by 4 SNR max = E
c ( dpcch ) N t .times. P margin P dpcch .times. f (
i = 1 n TPC i )

[0096] where f(.) is a function of accumulated TPC bits in linear scale.
The maximum (Eb/I.sub.0).sub.i for each MS.sub.i is then given by 5 (
E b I 0 ) i , max = SNR max .times. PG

[0102] .lambda..sub.v/.mu..sub.v=Voice Erlangs which is defined as the
ratio of average voice arrival rate to average time per voice call.

[0103] .lambda..sub.d1/.mu..sub.d1=Data Erlangs which is defined as the
ratio of average data arrival rate to average time per data call for a
pool of users using data rate R.sub.d1.

[0104] .mu..sub.d2/.mu..sub.d2=Data Erlangs which is defined as the ratio
of average data arrival rate to average time per data call for a pool of
users using data rate R.sub.d2.

[0105] .rho..sub.v=Expected value of voice activity factor.

[0106] .beta.=1n(10)/10.

[0107] .sigma..sub.v, .sigma..sub.d1 and .sigma..sub.d2=Power control
standard deviation for voice and data respectively.

[0108] The aggregate (E.sub.b/I.sub.o).sub.agg, computed from equation
(11-13) is then used (such that the noise rise and persistence p is
satisfied) in conjunction with the instantaneous throughput vs. Eb/Io
curves for each data rate (also known as static hull curves) and
aggregate MS buffer size to determine the maximum data rate or
P.sub.margin.sub..sub.--.sub.limit.sub..sub.--.sub.auto that can be
supported by the MS's in autonomous mode as described further below.

[0109] The BTS can then compute persistence (p). Given the number of voice
and data users and the allowable noise rise, the value of persistence can
easily be computed from equation (14). Alternatively, given the
persistence, allowable noise rise and number of voice users the number of
autonomous data users that can be supported at a particular rate can also
be calculated from equation (14).

[0110] In the MS, for the no soft handoff case, each MS decodes the
S-CCPCH to find out the value of p and the P.sub.margin.sub..sub.--.sub.l-
imit.sub..sub.--.sub.auto transmitted by BTS. The MS only decodes the FACH
send on the S-CCPCH when it has data in its buffer. The MS transmits only
in pre-defined sub-frames in the autonomous mode. The sub-frames in which
a MS is allowed to transmit in autonomous mode is set up by the scheduler
or RNC. Each MS desiring to transmit, transmits the data at a rate
proportional to P.sub.margin.sub..sub.--.sub.limit.sub..sub.--.sub.auto
with a probability p at the pre-allocated sub-frames. If the MS fails to
transmit (with a probability (1-p)), it waits a random amount of time
(exponential backoff with backoff timer dependent on the MS state) and
transmits the data with the new P.sub.margin.sub..sub.--.sub.limit.sub..s-
ub.--.sub.auto and new persistence probability at the pre-allocated
sub-frames.

[0111] In the soft handoff case, each MS decodes the FACH sent on the
S-CCPCH from all the Active Set BTS's for every active frame and stores
the persistence p.sub.i and the (P.sub.margin.sub..sub.--.sub.limit.sub..-
sub.--.sub.auto).sub.i transmitted by each Active Set BTS i. The MS then
determines p and P.sub.margin.sub..sub.--.sub.limit.sub..sub.--.sub.auto
by computing p=MIN(p.sub.1, P.sub.2, . . . ) and P.sub.margin.sub..sub.---
.sub.limit.sub..sub.--.sub.auto=MIN[(P.sub.margin.sub..sub.--.sub.limit.su-
b..sub.--.sub.auto).sub.1, (P.sub.margin.sub..sub.--.sub.limit.sub..sub.---
.sub.auto).sub.2, . . . ) where the numerical subscript denotes a
particular Active Set BTS. The MS transmits only in pre-defined
sub-frames in the autonomous mode. The sub-frames in which a MS is
allowed to transmit in autonomous mode are set up by the scheduler or
RNC. Each MS desiring to transmit, transmits the data at a rate
proportional to P.sub.margin.sub..sub.--.sub.limit.sub..sub.--.sub.auto
with a probability p at the pre-allocated sub-frames. If the MS fails to
transmit (with a probability (1-p)), it waits a random amount of time
(exponential backoff with backoff timer dependent on the MS state) and
transmits the data with the new P.sub.margin.sub..sub.--.sub.limit.sub..s-
ub.--.sub.auto and new persistence probability at the pre-allocated
sub-frames.

[0112] In this embodiment, the present invention addresses an efficient
way of changing the P.sub.margin.sub..sub.--.sub.limit.sub..sub.--.sub.au-
to ratio using the broadcast channel when the MS is transmitting in the
autonomous mode. This avoids performance degradation of the dedicated
channel and also defining a new frame format to support enhanced uplink
channel if P.sub.margin.sub..sub.--.sub.limit.sub..sub.--.sub.auto was
transmitted using a dedicated channel. Using the persistence value (p)
transmitted on the broadcast channel, the MS can control the reverse link
interference. The present invention also describes having the MS transmit
in autonomous mode in predefined n consecutive sub-frames only
(asynchronous nature of MS). The sub-frames in which MS is allowed to
transmit in autonomous mode are assigned by the RNC.

[0113] The RNC needs to signal the TFCS subset to be used by the MS
through RRC signaling to individual MSs, in order to minimize the MS's
data transmission from significantly degrading the performance of voice
users in the system. Through the techniques detailed in the present
invention, this is accomplished through more efficient signaling using a
broadcast to all users. Even if the dedicated control channel is used to
convey the information the signaling is more efficient on the RNC-to-BTS
(or RNC-to-Node B) interface due to it being sent to a BTS to be used for
all users in that BTS.

[0114] While the present invention has been particularly shown and
described with reference to particular embodiments thereof, it will be
understood by those skilled in the art that various changes may be made
and equivalents substituted for elements thereof without departing from
the scope of the invention as set forth in the claims below. Accordingly,
the specification and figures are to be regarded in an illustrative
rather then a restrictive sense, and all such changes and substitutions
are intended to be included within the scope of the present invention.

[0115] Benefits, other advantages, and solutions to problems have been
described above with regard to specific embodiments. However, the
benefits, advantages, solutions to problems, and any element(s) that may
cause any benefit, advantage, or solution to occur or become more
pronounced are not to be construed as a critical, required, or essential
feature or element of any or all the claims. As used herein, the terms
"comprises," "comprising," or any variation thereof, are intended to
cover a non-exclusive inclusion, such that a process, method, article, or
apparatus that comprises a list of elements does not include only those
elements but may include other elements not expressly listed or inherent
to such process, method, article, or apparatus.